Triangles • Triangle: a figure formed when 3

noncollinear points are connected by segments.

• Components of a triangle:– Vertices: A, B, C– Sides: AB, BC, AC– Angles: A, B, C

A C

B

Triangles can be classified by Angles:

1) Acute - 3 acute angles

2) Obtuse - 1 obtuse angle

3) Right - 1 right angle

A C

B

A C

B

A C

B

• or Sides:

• 1) Scalene - no sides congruent

• 2) Isosceles - at least 2 sides congruent

• 3) Equilateral - all sides congruent

A C

B

A C

B

A

C

B

Focus on Isosceles Triangles

• Vertex angle: the angle formed by the congruent sides

C• Base: the side opposite the

vertex angle

• Legs: the two congruent sides

and• Base Angles: the two angles

formed by the base and one of the congruent sides

A and B

A

C

BAB

AC BC

ApplicationFind d and the measure of each side of

equilateral triangle KLM if

KL = d + 2

LM = 12 - d

KM = 4d - 13

Triangles on the Coordinate Plane

Classify RST by sides

R (-1, -3)

S (4, 4)

T (8, -1)

2 2

2 1 2 1d x x y y